[clang-tools-extra] [include-cleaner] Unify symlink handling (PR #102615)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-x86_64-sie-win` running on `sie-win-worker` while building `clang-tools-extra` at step 7 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/46/builds/3166

Here is the relevant piece of the build log for the reference:
```
Step 7 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'clangIncludeCleaner Unit Tests :: ./ClangIncludeCleanerTests.exe/14/44' FAILED ********************
Script(shard):
--
GTEST_OUTPUT=json:Z:\b\llvm-clang-x86_64-sie-win\build\tools\clang\tools\extra\include-cleaner\unittests\.\ClangIncludeCleanerTests.exe-clangIncludeCleaner Unit Tests-2888-14-44.json GTEST_SHUFFLE=0 GTEST_TOTAL_SHARDS=44 GTEST_SHARD_INDEX=14 Z:\b\llvm-clang-x86_64-sie-win\build\tools\clang\tools\extra\include-cleaner\unittests\.\ClangIncludeCleanerTests.exe
--

Script:
--
Z:\b\llvm-clang-x86_64-sie-win\build\tools\clang\tools\extra\include-cleaner\unittests\.\ClangIncludeCleanerTests.exe --gtest_filter=PragmaIncludeTest.IWYUExportBlock
--
Z:\b\llvm-clang-x86_64-sie-win\llvm-project\clang-tools-extra\include-cleaner\unittests\RecordTest.cpp(542): error: Value of: PI.getExporters(FM.getFile("private1.h").get(), FM)
Expected: has 2 elements and there exists some permutation of elements such that:
 - element #0 file named (N: "export1.h"), and
 - element #1 file named (N: "normal.h")
  Actual: { 000001298898F0D8, 000001298898F018 }, where the following matchers don't match any elements:
matcher #0: file named (N: "export1.h"),
matcher #1: file named (N: "normal.h")
and where the following elements don't match any matchers:
element #0: 000001298898F0D8,
element #1: 000001298898F018

Z:\b\llvm-clang-x86_64-sie-win\llvm-project\clang-tools-extra\include-cleaner\unittests\RecordTest.cpp(544): error: Value of: PI.getExporters(FM.getFile("private2.h").get(), FM)
Expected: has 1 element and that element file named (N: "export1.h")
  Actual: { 000001298898F0D8 }, where the following matchers don't match any elements:
matcher #0: file named (N: "export1.h")
and where the following elements don't match any matchers:
element #0: 000001298898F0D8

Z:\b\llvm-clang-x86_64-sie-win\llvm-project\clang-tools-extra\include-cleaner\unittests\RecordTest.cpp(546): error: Value of: PI.getExporters(FM.getFile("private3.h").get(), FM)
Expected: has 1 element and that element file named (N: "export1.h")
  Actual: { 000001298898F0D8 }, where the following matchers don't match any elements:
matcher #0: file named (N: "export1.h")
and where the following elements don't match any matchers:
element #0: 000001298898F0D8


Z:\b\llvm-clang-x86_64-sie-win\llvm-project\clang-tools-extra\include-cleaner\unittests\RecordTest.cpp:542
Value of: PI.getExporters(FM.getFile("private1.h").get(), FM)
Expected: has 2 elements and there exists some permutation of elements such that:
 - element #0 file named (N: "export1.h"), and
 - element #1 file named (N: "normal.h")
  Actual: { 000001298898F0D8, 000001298898F018 }, where the following matchers don't match any elements:
matcher #0: file named (N: "export1.h"),
matcher #1: file named (N: "normal.h")
and where the following elements don't match any matchers:
element #0: 000001298898F0D8,
element #1: 000001298898F018

Z:\b\llvm-clang-x86_64-sie-win\llvm-project\clang-tools-extra\include-cleaner\unittests\RecordTest.cpp:544
Value of: PI.getExporters(FM.getFile("private2.h").get(), FM)
...

```

https://github.com/llvm/llvm-project/pull/102615